(1): A critical review indicated that magnetic resonance imaging can be used to identify and quantify changes in brain volume in relation to human aging and dementia. (2): Analysis of volumetric magnetic resonance imaging data demonstrated differences in the extent of atrophy of the hippocampus-amygdala formation and of the corpus callosum atrophy in patients with Alzheimer disease as a function of dementia severity. The analysis method provides a statistical framework to identify atrophy patterns of different brain structures in human neurodegenerative diseases. (3): In vivo imaging methods (positron emission tomography (PET), structural and functional magnetic resonance imaging), allow us to examine human brain function and structure in relation to healthy aging, and to diagnose and understand the different causes of dementia, including Alzheimer disease. Functional or pharmacological activation ('stress' tests) with in vivo imaging are particularly useful in this regard. (4): A theory for how Darwinian competition among kinships rather than only among individuals was proposed to explain how cognitive ability, brain size and life span co-evolved during primate evolution.